This invention relates to improvements in the structure railway cars for carrying metal coils, commonly referred to as coil cars.
Coils of steel sheet are often carried by rail cars. Coils can be mounted either longitudinally or transversely. In a longitudinal mounting, the axis of revolution of the coil is aligned to be substantially parallel with the rolling, or longitudinal, direction of the rail car. A longitudinal mounting often has the appearance of a single long trough with a number of moveable intermediate dividers. In a transverse mounting, the axis of revolution of the coil is aligned across the tracks, that is, perpendicular to the rolling direction of the rail car. Transverse mounting cars have a number of parallel bunks, rather than one long trough. A bunk is generally V-shaped, and the coil sits in the bunk with the outer circumference of the coil tangent to the V at two points such that it cannot roll. The V-shaped bunks are generally lined with wood decking to act as cushioning, thereby discouraging damage to the coils during loading or travel.
In earlier times flat cars were converted to function as coil cars by adding bunks on to the flat car deck to prevent the coils from rolling off the deck during transport from the rolling mill to the customer. The basic structure of a flat car includes a main center sill that is box shaped in cross-section. The center sill of this kind of car is the main structural member of the car and runs from one end coupling of the car to the other. The center sill is the primary load path of the car both for longitudinal buff and draft loads from coupler to coupler, and for carrying the vertical load bending moment between the trucks. A wide deck is mounted above the center sill of this kind of car. Often, alternating cross-bearers and cross ties extend outwardly from the central sill. The cross bearers tend to be of deeper section and provide the majority of the support for the outboard regions of the deck.
Over time, the size and weight of coils that can be carried has increased. The flat car design has evolved to have stronger and bigger main sills, sometimes reinforced by doubled sections. Further, the central sill may not necessarily be of constant section, but may have a xe2x80x9cfish bellyxe2x80x9d profile. That is, the depth of section of the centre sill can increase toward the mid-section of the railcar to correspond to the increase in bending moment at mid-span between the rail car trucks. Further, longitudinal stringers, in the form of I-beams or wide flange beams have been located above the deck level to form the upper lip of the longitudinal bunk. In another step in the evolution of the flat car design, some or all of the flat decking can be replaced by canted decking to form the V-shaped trough. In more recent times the flat decking has been removed entirely, to leave a railcar having a dominant centre sill, a pair of elevated outboard longitudinal beams, cross-bearers cantilevered out from the centre sill like ribs; and V-shaped decking to form the trough.
The present inventor has taken a different approach. Rather than having a dominant center sill, the inventor employs a pair of outboard beams of relatively deep section. The coil carrying bunk is then supported at its lateral ends to extend between the two deep side beams. A car with a pair of deep beams, well separated also has superior lateral bending resistance to a narrower car.
In terms of fabrication, it is advantageous to reduce the number of different parts used in an assembly. To that end, it would be advantageous to replace the traditional arrangement of alternating cross-ties and cross-bearers with a single design of cross-bearer. When the cross-bearer is designed conceptually as a cantilevered arm or rib, it is not uncommon for the root of the arm to be of a deeper section than the tip, reflecting the relatively large moment that must be carried at the root of the arm. However, a tapered section is not as convenient as a section of constant depth. A section of constant depth can be produced by a rolling mill, and is less likely to have welding defects or irregularities than a fabricated section. By contrast, when the cross-bearer is in concept more akin to a beam supported at two ends, the use of a section of constant depth is not inappropriate.
The use of a deep side beam presents the opportunity for improving the connection at the outboard tips of the cross-bearers. Formerly, the use of I-beam or wide flange beams at the upper and outer lips of the trough did not always present a convenient welding arrangement. The cross-bearer end could be trimmed to match the profile of the I-beam web, or the flange of the I-beam could be trimmed back locally to accommodate the cross-bearer tip. In either case the cross-bearer tip would butt against the I-beam section. When deep side beams are used, the beams themselves have intermediate vertical stiffeners to discourage the relatively thin webs of the beams from buckling. At the same time, the stiffeners present a flat surface, in the same plane as the plane of the web of the cross-bearer, against which a lap joint can be formed. Not only can a better joint be formed, but the fit-up process in manufacturing is, in the view of the present inventor, easier. That is, the pre-existing vertical stiffener of the beam acts as a longitudinal stop for the outboard tip of the cross-bearer, automatically locating it in the correct position.
Access for brake maintenance on a car with deep side walls may be limited. To address this concern the present inventor has eased the downward profile of the side beams to permit improved access to the brakes between the trucks and the mid-span portion of the car.
The present invention provides, in a first aspect, a rail car for carrying metal coils, comprising a pair of end structures each mounted on a rail car truck, a pair of side beams extending between the end structures, and a transverse cradle, for cradling metal coils, mounted between the side beams. The cradle has a longitudinally extending low central portion. The lowest point of the low central portion lies at a height that is at least as high as the lowest extremity of the side beams.
In an additional feature of that aspect of the invention, the railcar has, at a transverse-section between said trucks, a second moment of area about a horizontal neutral axis, and the side beams contribute at least half of the second moment of area of the section. In another additional feature of that aspect of the invention, the side beams of the rail car contribute at least three quarters of the second moment of area of the section. In a still further additional feature of that aspect of the invention, the side beams of the railcar contribute at least 90% of the second moment of area.
In still another further additional feature of that aspect of the invention, at a transverse section between the trucks, the location of the maximum longitudinal tensile stress under a gravity load is in the lowest chord of one of the side beams.
In yet another additional feature of that aspect of the invention, at a transverse section between the trucks, the location of maximum longitudinal compressive stress under a gravity load is in the highest chord of one of the side beams. In still another additional feature of that aspect of the invention, the cradle has a center sill extending longitudinally along the low central portion.
In still yet another additional feature of that aspect of the invention, the central sill has a top flange and a bottom flange, the rail car has, at a transverse section between the trucks, a neutral axis for bending under gravity loads, and the neutral axis lies at a height that is between the height of the top and bottom flanges.
In another additional feature of that aspect of the invention, the cradle includes cross-bearers connected to the side beams. In still yet another feature of that aspect of the invention, in at least a medial portion of the rail car between the trucks, the cross bearers are of substantially uniform design. In a further feature of that aspect of the invention, at least a medial portion of the rail car between the trucks is of the type chosen from the set of rail car types consisting of rail car portions that are free of cross-ties and rail car portions in which the number of cross ties is fewer than two thirds as many as cross bearers.
In still a further additional feature of that aspect of the invention, the rail car has a through centre sill of substantially constant cross-section. In still yet a further additional feature of that aspect of the invention, over at least the medial portion of the rail car, the cross-bearers are of substantially uniform design. In another further additional feature of that aspect of the invention, at least the medial portion of the rail car is of a type chosen from the set consisting of types that are free of cross-ties, and types that have less than two-thirds as many cross-ties as cross-bearers.
In another aspect of the invention, there is a rail car for carrying metal coils comprising a pair of end structures each mounted on a rail car truck, a pair of side beams extending between the end structures, a transverse sling, for cradling metal coils, slung between the side beams, the rail car having a set of brakes, and at least one of the side beams having a relief permitting access to the brakes.
In an additional feature of that aspect of the invention, the relief is located adjacent the truck. In another additional feature of that aspect of the invention, the one beam has a relief adjacent each of the trucks. In still another additional feature of that aspect of the invention, both the beams have reliefs adjacent the trucks.